[SPARK-49509][CORE] Use Platform.allocateDirectBuffer instead of ByteBuffer.allocateDirect

### What changes were proposed in this pull request?
This PR aims to use `Platform.allocateDirectBuffer` instead of `ByteBuffer.allocateDirect`.

### Why are the changes needed?
apache#47733 (review)

Allocating off-heap memory should use the `allocateDirectBuffer` API provided `by Platform`.

### Does this PR introduce _any_ user-facing change?
No

### How was this patch tested?
GA

### Was this patch authored or co-authored using generative AI tooling?
No

Closes apache#47987 from cxzl25/SPARK-49509.

Authored-by: sychen <sychen@ctrip.com>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

Author: cxzl25

core/src/main/java/org/apache/spark/io/NioBufferedFileInputStream.java

@@ -17,6 +17,7 @@
 package org.apache.spark.io;
 
 import org.apache.spark.storage.StorageUtils;
+import org.apache.spark.unsafe.Platform;
 
 import java.io.File;
 import java.io.IOException;
@@ -47,7 +48,7 @@ public final class NioBufferedFileInputStream extends InputStream {
   private final FileChannel fileChannel;
 
   public NioBufferedFileInputStream(File file, int bufferSizeInBytes) throws IOException {
-    byteBuffer = ByteBuffer.allocateDirect(bufferSizeInBytes);
+    byteBuffer = Platform.allocateDirectBuffer(bufferSizeInBytes);
     fileChannel = FileChannel.open(file.toPath(), StandardOpenOption.READ);
     byteBuffer.flip();
     this.cleanable = CLEANER.register(this, new ResourceCleaner(fileChannel, byteBuffer));

core/src/main/scala/org/apache/spark/storage/DiskStore.scala

@@ -35,6 +35,7 @@ import org.apache.spark.internal.LogKeys._
 import org.apache.spark.network.buffer.ManagedBuffer
 import org.apache.spark.network.util.{AbstractFileRegion, JavaUtils}
 import org.apache.spark.security.CryptoStreamUtils
+import org.apache.spark.unsafe.Platform
 import org.apache.spark.unsafe.array.ByteArrayMethods
 import org.apache.spark.util.Utils
 import org.apache.spark.util.io.ChunkedByteBuffer
@@ -324,7 +325,7 @@ private class ReadableChannelFileRegion(source: ReadableByteChannel, blockSize:
 
   private var _transferred = 0L
 
-  private val buffer = ByteBuffer.allocateDirect(64 * 1024)
+  private val buffer = Platform.allocateDirectBuffer(64 * 1024)
   buffer.flip()
 
   override def count(): Long = blockSize

core/src/main/scala/org/apache/spark/util/DirectByteBufferOutputStream.scala

@@ -57,7 +57,7 @@ private[spark] class DirectByteBufferOutputStream(capacity: Int) extends OutputS
     if (newCapacity < minCapacity) newCapacity = minCapacity
     val oldBuffer = buffer
     oldBuffer.flip()
-    val newBuffer = ByteBuffer.allocateDirect(newCapacity)
+    val newBuffer = Platform.allocateDirectBuffer(newCapacity)
     newBuffer.put(oldBuffer)
     StorageUtils.dispose(oldBuffer)
     buffer = newBuffer